It was a risk for director Richard Linklater to go so dark in "Before Midnight," the latest round of the romantic musings he began with his stars, Julie Delpy and Ethan Hawke, nearly 20 years ago. The illusions of a more pristine love in "Before Sunrise" have been shelved so that the tipping point in a relationship can be laid bare. A devastating fight is the centerpiece now, the teasing flirtations a distant memory.

Though the gauzy beauty of the earlier films remains, as does a sun-drenched European setting, this time Greece, what you will remember, what you will feel compelled to talk about long after, is the fight. It sears with an intensity that rivals another classic battle between the sexes, "Who's Afraid of Virginia Woolf?"

Though you needn't have seen the earlier films, it helps to know how it began. Jesse (Hawke) and Celine (Delpy) were strangers on a Budapest to Paris train. Young, beautiful, bright, both having a serious go at adulthood but carefree enough to seize the moment and steal off for a few hours to fall in love. They would wander through Vienna, carried along by the exhilaration of a sensual connection, their conversation dancing around cultural differences — she's French, he's American — and gender politics with incredible grace.

Linklater's cinéma vérité style created an immediate intimacy, setting the tone for the films that would follow. The dialogue — meticulously scripted but effortless in its delivery — captured the cynicism and romanticism of the young. The actors — rarely out of frame — were strikingly precise in the casual exchanges. The disparate pieces jelled beautifully and marked the film as something special.

Now, two films later in "Before Midnight," the clock is ticking more ominously, the conversation is sometimes strained and the love is more confined. The romantic ideal has given way to the routine.

They are still beautiful, though weathered, and still talking, but Celine and Jesse have lives that look more like the ones they swore never to have in 1995's "Sunrise"; ones they were still resisting nine years later in "Before Sunset," when they reconnected at a Paris book signing for the novel Jesse wrote about their Vienna affair.

A desire to escape squabbling spouses first brought them together on the train. In "Midnight" they are the couple and their fights are toxic. Which might sound like a complaint, but it's not. If anything, the films have only gotten better by letting the relationship marinate. "Midnight's" more disgruntled edge reflects what creeps up on couples as years pass, regrets stack up, kids factor in, real life intervenes.

The movie's opening scene is a familiar one in a time of divorce and blended families. The setting is the Kalamata Airport in Greece. Jesse is saying his final goodbyes to son Hank (Seamus Davey-Fitzpatrick) before putting him on a plane back to the States where he lives with his mom.

The father fears he is missing too much of his son's life; the 13-year-old is sensitive to his parents' strained relationship. Hawke turns the moment into a case study of those competing sides of caring and guilt, the smile dimmed by a worried brow, the quick squeeze of Hank's shoulder.

Summer is at an end as well, and the sabbatical the writer has had with his family in Greece is coming to a close. With Hank packed off, Jesse and Celine head back for a final dinner at their host's, an older expat named Patrick (Walter Lassally). As their twin daughters doze in the back seat of the car, they talk.

It is what the two characters have always done so well. At first it feels as if we're catching up with old friends; the car creates both a close and a closed environment. The themes that run through all the films — on religion, gender politics, love and careers — have gotten less philosophical and more specific. Linklater, Hawke and Delpy have in turn sharpened the dialogue, making it far more pointed.

The first drop of acid comes when Jesse floats the idea of moving the family from Paris to Chicago to be closer to Hank. Celine's just gotten a sizable job offer and the idea of giving up this career chance and uprooting the girls becomes a flash point. This is how couples separate, she snaps at one point.

Despite the shadows that are deepening, the luminous quality has not been lost. The country home where they're staying could hardly be more picturesque. Much of the dinner talk is about their storied romance. They've been given a parting gift — a night in a hotel sans kids, and theoretically sans worry. That there will be sex seems a given.

But once inside the room, the tonal quality of the film shifts and a fight soon begins. As is often the case, the reason for the fight is not the real reason for the fight. That you know it immediately is part of the film's brilliance.

The fight itself is unflinching in its truth-telling. So wounding are the words, so naked is the pain, so naked is Delpy, half-undressed and seemingly unaware of anything beyond channeling Celine's anger, you may fear you'll be asked to take sides.

It's an extraordinary scene, disappointments used to flail each other; nothing is off limits. Egos are roasted like pigs on a spit. Ids are destroyed. Delpy and Hawke have been digging around their characters so long, they know the emotional triggers and exactly how to play them.

Linklater, Delpy and Hawke — with a creative collaboration that has more history than Jesse and Celine — were in an ideal position to get inside a relationship that, like its characters, is showing its age. They risked all to take it to its hellish edge. But isn't that what artists are supposed to do? Challenge themselves? Challenge us?